Okay, I scoured the island for all that I could, so I think that I have all the evidence gathering that I can get. I suppose it is trial time, or more accurately trial time the next time I play. Starlight conveniently lists all of the crimes and evidence by character. I'm assuming that I will be going through all of the crimes, so I will go through each one in reverse order, since the first one listed is the major one, and say who I think the culprit is:
The Murder of Grace Bloodlines Carmelina by default since she directed Akiko to leave for some reason, Henry didn't have a blade to carve into Grace, and Akiko didn't wear a ring
The Mystery of the Dead Killer Demon Witness not only has an overwhelming amount of evidence, but the key one of him contacting an ID with the same combination as that of the crate holding a demon is pretty much having him dead to rights
Who Opened the Third Seal This is when this swerve of a new character Dainonigate, late in the game, which I can't say that I am a fan of, starts to muck up the crimes. I think this is Sam though as he both almost certainly stole the blood and knew of a blood lock
The Second Holy Seal Lydia's perfume, which she has said she makes herself and only for herself, is pretty damning while the presence of petals from potentially Yuri's hat can be more easily planted. Tire tracks and her tablet also present at key locations makes it hard to believe that it isn't her.
Who Kills the Holy Seal Marshals I think this was Akiko. I was about to say Lydia again, but I changed my mind after realizing that Lydia took the back entrance to where the holy seal was at, so she shouldn't have come into contact with the fake marshals in front of the building. They are clearly the prisoners she signed out and not marshals, but I am not certain about the motive here. I may remember finding out that Marshals are not immortal and thus do not move on to new paradises, so maybe she was trying to find a way to keep her lover, Voth, from dying? I don't know what her next step would be, but that's the best I can come up with.
Who Breached the Fourth Holy Seal Okay, now I am forgetting what the fourth holy seal was. Was it just before the room where the council and crated demon died? If so, it could be anyone, but based on the bombshell of portals presumably used by Carmelina and Dainonigate, it would be easier for them than the likes of Sam or Marshall (maybe I shouldn't be totally dismissive of Henry). There is hardly any evidence for this one though and Carm/Dai's is especially light. It feels like it has to be one of Witness/Sam then. If Sam/Lydia opened the other seals like I suspect, I guess I should stick with that narrative and say Sam even though I have no other evidence.
Henry's Demonic Possession It was clearly Yuri with the book checking out. There is nobody else to consider.
Henry's Escape There are persuasive arguments against either Akiko or Witness. It could honestly be something they teamed up for, but for the sake of choosing one, I say Witness because I found that aural advice on the beginning island pointed toward where Henry was locked up. He has the stronger link to that as he could use the death screams of the slaves being sacrificed to cause an adrenaline rush in Henry, something that he learned from Dr. Jazz.
K. HX is Missing If it weren't for the drag marks, I would say suicide. Akiko and Yuri have some connection with having him repair pieces of jewelry for them, but that's really it. Crimson has the much stronger relation to K. HX and his demise with her using him and him being obsessed with her. This could have gone down a number of ways for a number of reasons, but at the very least, it seems highly likely that Crimson at least dragged and dumped the body over the cliff.
The Crime to End All Crimes Dainonigate had to have been the muscle and Carmelina had to have been the mastermind behind this. Carmelina seemed to have an idea of what Witness was up to and probably used that to carry out her plan to be able to pin the murder on either Henry or the demon, but the four portals I discovered and where they led to (Carmelina's, fourth seal, Witness, Dai's bunker/prison thing, and I forget the other if there was one), mean it has to be them.
I'm realizing that most of these are probably pretty obvious and didn't need to make this giant post, but I already went through the effort, so whatever I am posting it.
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KCF can't actually be a real person but he is - greengravy